Not sure if you know this or have tried it, but if you take a wire (while unit is completely unplugged) and hold one end to ground and then simply drag it across ALL the rom chips (obviously you have to open the unit up and access the chips) legs, one at a time (and it can be rather quickly) it will "usually" discharge any bad or locked rom information that might keep the unit from proper power up enumeration...simply take one end of the wire to a ground screw and drag it across all the chip legs (try to keep it only on one leg at a time)...then put the unit back together and power it up...most of the newer chips have a register that when you reset a certain pin to ground they default to and in a burned in chip it is pretty simple to do this.
It is a fast way to see if you've "bricked it"